Disposable absorbent garments such as infant diapers or training pants, adult incontinence products, and other such products are well-known in the art. Typically, the chassis of such absorbent garments comprises a liquid-permeable body-contacting liner sheet (or “top sheet”), a liquid-impermeable backing sheet (or “back sheet”), and a moisture-absorbent core (or “absorbent core”). The absorbent core usually is made of a nonwoven mat of randomly arrayed fiber and super absorbent polymer (“SAP”) and generally is disposed between the top sheet and the back sheet.
The absorbent core may be purchased as bulk roll goods or may be formed from fiberized fluff pulp and SAP particles in a forming chamber, and encased in a liquid pervious wrap to stabilize the layer or layers of the core. In the general practice of forming fibrous materials into absorbent cores, it is common to utilize a fibrous sheet of cellulosic fibers, or other suitable fibers, which is fiberized in a conventional fiberizer or other device to form discrete fibers. The discrete fibers then are entrained in an air stream or airflow along with an amount of SAP particles and directed to a forming surface where the fibers and SAP particles are deposited to form a pad of fluff, (i.e. a non-woven mat of randomly arrayed fibers containing interstitial void space and being highly compressible in character). The forming surface rotates at a speed adjusted as necessary to form the desired thickness of the pad of fluff, which is removed as a continuous sheet from the forming surface for tissue wrapping and absorbent core formation.
Typically, the air stream with the entrained discrete fibers is directed into one end of a forming chamber, where a forming surface is located on the other end of the forming chamber. The SAP particles usually are introduced into the forming chamber downstream of the point from where the discrete fibers are introduced, yet upstream of the forming surface. The SAP particles and discrete fibers mix in the air flow in the forming chamber before they reach the forming surface. The nozzle used to introduce the SAP particles into the forming chamber typically was configured to have a straight nozzle with a funnel end, and the SAP particles usually were fed into the funnel end. Typically, the funnel was disposed at about a 20 degree angle from level, or 20 degrees from a horizontal position.
The forming surface utilized in such systems typically was constructed as a wire or screen grid and typically employed pneumatic flow means such as a vacuum suction apparatus to define a differential pressure zone on the forming surface and impose a pressure differential thereon. The air entrained fiber and SAP particle stream would pass through the openings or perforations in the screened grid of the forming surface. The use of vacuum suction to draw the air entrained fiber and SAP particles stream to the forming surface, with the passage of the air component through the forming surface, is highly efficient and lends itself to high speed commercial operations. A typical configuration for feeding SAP particles to an airstream containing fibers, and then to a forming rotating drum is disclosed in U.S. Pat. No. 6,139,912, the disclosure of which is incorporated by reference herein in its entirety.
The SAP particles and the fibers typically did not mix homogeneously while inside the forming chamber to form a well-mixed pad of fluff on the forming surface, when using previous operating conditions and web forming configurations. Thus, the absorbent cores made from this pad of fluff tended to have uneven layers of SAP particles and fibers. This non-homogenous layering of the SAP particles and the fiber reduced absorbent core performance, as measured according to techniques well known in the art.